I think it took me around 2-3 weeks to get it down consistently. When I was teaching kids how to yoyo, I do remember from videos that mentioned curl your arm like your flexing and showing your biceps, but what I told the kids to first do it getting the hang that a yoyo will be going parallel to your shoulders. Although it may sound weird, I would first have the twist their upper body to the direction of where they’re wanting to throw, twist right if you’re right handed, left if you’re left handed. And you’ll throw a typical sleeper, but instead of it going to the same side as your throw hand, but now to go parallel to where your feet is placed. At first the angle will be not exactly parallel, but I felt this way gave your body a feel of how a different way of travel that aren’t frontal type tricks.
Once you get used to the way the yoyo travels, doing the arm flexing thing comes much easier to transition into.
I hope this works…I know it may sound weird.